The company, along with business partner Altaeros Energies, which built the balloon (pictured), carried out the test at Japan’s Hokkaido Spaceport, at an altitude of 249m.
The test “successfully achieved stable and wide-area network coverage with this system”, said SoftBank in a statement.
SoftBank’s HAPSMobile – based on an abbreviation for high altitude platform station – has been working on flying base stations for some time. In 2020 it successfully transmitted 4G mobile signals – including a video call – from an uncrewed solar-powered aircraft 19km above New Mexico.
But the research programme identified a challenge: “that the communication area projected to the ground cannot be fixed because the footprint shifts as the aircraft turns”, SoftBank said last year.
There’s also a problem when using an array of balloons, especially when they are deployed after a disaster. “The communication area, or footprint, projected to the ground cannot be fixed because cells rotate as the aircraft turns, which in turn causes frequent handovers and affects reception strength levels, thereby impacting telecommunications quality.”
The latest trial aims to provide a stable footprint from each balloon. “By using a cylindrical antenna with digital beam-forming control, SoftBank’s footprint fixation technology secures the cell footprint on the ground by controlling the direction of radio beams as the airborne vehicle rotates, which is essential for airborne wireless telecommunications platforms,” said the company.
In the Hokkaido trial, SoftBank and Altaeros used an “AI-based, three-tether control system that can control and stabilize the aerostat [the balloon] at altitudes of up to 305m”. This is far less than the New Mexico trial in 2020, but was enough “to enable wide-area network coverage”, they said. “Under good line-of-sight, [that achieves] wide-area network coverage of a few tens of kilometres.”
They used an autonomous aerostat autopilot system and the balloon delivered “stable network coverage regardless of aerostat rotation, motion and pitch/yaw thanks to footprint fixation technology”, they said.
Now, SoftBank said it “will study ways of utilizing its acquired knowhow and data for application to its telecommunication network disaster preparedness and the construction of HAPS-based telecommunication platforms”.
